A. Field of the Invention
The invention relates to a method and apparatus for improving semiconductor processing equipment, and more specifically, to a method and apparatus for preventing a horizontal quartz tube located in a furnace module from bending due to high temperature and gravity.
B. Description of the Prior Art
A conventional semiconductor processing equipment includes four parts: source cabinet 11, furnace module 12, load station 13, and controller 14, as shown in FIG. 1. Furnace module 12 contains horizontal quartz tube 101 for processing wafers. The outside wall of horizontal quartz tube 101 is surrounded with heating element 102 for heating wafers inside. Load station 13 is a wafers transfer system which can load wafers 103 into horizontal quartz tube 101. Wafers 103 are placed on top of boat 104 to be delivered by paddle 105 into horizontal quartz tube 101. Source cabinet 11 contains gas piping (not shown in FIG. 1) and a mass flow controller (not shown in FIG. 1). At the closed end of horizontal quartz tube 101, there is an inlet pipe 106 of a gas injector which injects high purity gases into horizontal quartz tube 101 such as, O.sub.2, H.sub.2 O, HCL, TCA, TDCE, and so on. Controller 14 controls the factors of processing wafers such like, temperature, timing, air, and recipe.
FIG. 2A shows the schematic diagram of a conventional horizontal quartz tube. Referring to FIG. 2A, the inlet pipe of gas injector 202 is at the center of the closed end of horizontal quartz tube 201 for injecting high purity gases into horizontal quartz tube 201. At the bottom of horizontal quartz tube 201, there is a removable thermocouple sheath 203 inserted with a thermocouple for temperature measurement. FIG. 2B shows an enlarged detail of the part 205 where thermocouple sheath 203 is adjacent to horizontal quartz tube 201. As FIG. 2B shows, the inlet pipe 206 of thermocouple sheath 203 has a flat opening. The opposite end 207 of thermocouple sheath 203 as illustrated in FIG. 2C is closed so that the thermocouple inside will not be exposed to the air of horizontal quartz tube 201. Thermocouple sheath 203 is weld on horizontal quartz tube 201.
During the heating process, the temperature can reach about 1200.degree. C. Since the melting point of a conventional horizontal quartz tube is about 1300.degree. C., the high temperature and the weight of the horizontal quartz tube itself will cause the horizontal quartz tube to bend about 2 cm in the center in about one month. The distortion of horizontal quartz tube is large enough to break the wafers as the wafers are transferred to the horizontal quartz tube. Consequently, the horizontal quartz tube must be replaced every month. Currently, a horizontal quartz tube costs about $2,700 dollars. Suppose a Fab has nine such horizontal quartz tubes, the total cost for the replacement of horizontal quartz tubes will be as much as $291,600 dollars each year.
In addition to the replacement fee, the efforts and time devoted in replacing such horizontal quartz tubes must also be considered. For one thing, before the horizontal quartz tube can be safely removed, its temperature must be cooled down from 800.degree. C. to room temperature. The cooling procedure takes about 8 hours. Before a new horizontal quartz tube can start working, it needs to be installed that includes temperature adjusting, testing and many other things. So, the labor and time devoted in installing a horizontal quartz tube each time must also be counted. In general, the entire procedure for replacing a horizontal quartz tube takes over 24 hours. For another thing, during this time, all the jobs related to processing wafers in horizontal quartz tubes stay idle until the horizontal quartz tube is replaced. The frequent replacement of horizontal quartz tubes will certainly decrease the production rate of wafers. For these reasons, it is desirable to increase the lifetime of a horizontal quartz tube and minimize the time and effort devoted in replacing horizontal quartz tubes. More importantly, it is desirable to save the replacement fee.